Vibratory delay line having novel support



June 20, 1967 G. H. HARE 3,327,252

VIBRATORY DELAY LINE HAVING NOVEL SUPPORT Original Filed Oct. 28, 1963 3Sheets-Sheet 1 INVENTOR. George 1mm ATTOI2 EV June 20, 1957 HAREVIBRATORY DELAY LINE HAVING NOVEL SUPPORT 3 Sheets-Sheet 2 OriginalFiled Oct. 28, 1963 June 26, W67 G. H. HARE VIBRATORY DELAY LINE HAVINGNOVEL SUPPORT Original Filed Oct. 28, 1963 3 Sheets-Sheet 5 E EE 1UUnited States. Patent O 3,327,252 VIBRATORY DELAY LINE HAVING NOVELSUPPORT George H. Hare, Oakland, Calif., assignor to Friden, Inc., acorporation of Delaware Continuation of application Ser. No. 319,197,Oct. 28, 1963. This application Feb. 2, 1966, Ser. No. 533,750 23Claims. (Cl. 333-30) The present invention relates to elastic, oracoustic, delay lines. This application is a continuation of mycopending application for Delay Line, Ser. No. 319,197, filed Oct. 28,1963, and now abandoned.

v A delay line may include a rod or wire, along which an elastic signalwave travels. Such a line may be slender, with a length several thousandtimes its diameter, and so may require numerous supports along itslength. Heretofore, supports for such lines have exhibited a couplingwith said lines, and have markedly affected their transmissioncharacteristics. Such supports have added reactive loading, have causedattenuation, and have imposed frequency dispersion. Furthermore, suchsignal distortions and losses have increased with the pressures that thesupports exerted-on the lines. Consequently, a tight grip on the line bya support produced large distortion, and any acceleration forces, suchas those of shock and vibration, imposed unwanted modulation on thesignals.

It is an object of the present invention to overcome the foregoingdifficulties, and to provide a delay line with minimum distortion, andwith operating characteristics that have a minimum susceptibility tochange in response to shock, vibration, acceleration or spinningmotions.

A further object is the provision of a support for a delay line whichdoes not affect the operating characteristics of the line, or distortthe signals thereon.

A further object is the provision of a support for firmly holding adelay line while remaining operationally uncoupled therefrom, forsupporting it without participating in its operation.

It is a further object to provide a construction for a delay line inwhich the elongate elastic line maybe firmly clamped for supporting itagainst shock, vibration, acceleration, and centrifugal forces.

A further object is the provision of a clamping structure and materialtherefor which will firmly support an elastic delay line withoutrestricting its operation or imposing distortions of the signals.

Still a further object is the provision of a delay line that isdecoupled from, and numb, to its supports.

These and other objects and advantages of the present invention will beapparent from the following description of specific embodiments thereof,taken in connection with the accompanying drawings, wherein:

FIG. 1 is a perspective view of a delay line embodying my presentinvention.

FIG. 2 is an exploded perspective view of one of the support membersshown in FIG. 1.

FIG. 3 is a partial perspective view of a modification of the structureof FIG. 1.

' FIG. 4 is an elevational sectional detail of FIG. 3

FIGS. 5, 6 and 7 are partial elevational views of other supportstructures for the delay lines of FIGS. 1 and 3 FIGS. 8, 9 and 10 arepartial elevational views of clamping supports for the delay line ofFIG. 1; and

FIG. 11 is a pictorial view of a knife-edge clamp-ing support for adelay line.

The .delay line as shown in FIGS. 1 and 2 includes a spirally coiledwire 10 in which the wire is about .025 inch in diameter and thirty feetlong, and the coil has a mean diameter of about eight inches. The wire10 is composed of a nickel-iron alloy known as NiSpan, and is 3,32Patented J mice 20, 1967 here opera-ted in the torsional mode. At eachend of the wire 10, two magnetostrictive ribbons 12, each about .002 by.020 inch, are welded to the wire at diametrically opposite points ofits cylindrical surface. Each of these ribbons extends through atransducer coil 14 and then through an absorbing pad 18 composed ofpieces of rubber clamped against it. Permanent magnets 20 in holders 21provide a bias magnetization of the ribbons 12 within the coils 14. Asignal in the form of an electric current applied to the pair oftransducer coils 14 at one end of the wire 10 exerts opposite actions,contraction and expansion, on the two magnetostrictive ribbons 1 2,which actions are transmitted as waves along the ribbons. These oppositeactions operate as .a couple on the wire 10 and generate a torsionalstrain which travels as an elastic torsional wave along the wire 10. Atthe other end of wire 10, the wave is transmitted as opposite effects,contraction and expansion, to the ribbons 12 of the receivingtransducer, and induces voltage signals in the coils of the receivingtransducer in a known manner.

It is well-known that certain .materials, when laid against the elastictransmission member of a delay line, will alter the transmissioncharacteristics thereof. For example, rubber pads, such as pads 18 inFIG. 1, are commonly clamped to the extreme ends of such a line forabsorbing the signal and thereby preventing the appearance ofend-reflected signals in the output. While it has been necessary tosupport the elongate transmission line, usually a metal wire, thecontact of the supports with the wire has altered the output signal.Therefore, such supports have been arranged heretofore to exert aslittle pressure as possible on the wire and the number of such supportshas been kept to a minimum. The wire has lain loose in suchsupportswit-bout being clamped, and has been dependent on its own slightstiffness for holding itself in place. Delay lines so constructed havelacked mechanical ruggedness, and consequently have been incapable ofresisting severe vibration, shock, or other forces.

In accordance with my present invention I support the line with afaineant material and structure, that is, a material and structurecapable of clamping the wire without substantially affecting its signaltransmission characteristics. Such a material, though it may be firmlyclamped against the wire, or elastic delay element, remainssubstantially uncoupled therefrom with respect to its operation as anelastic signal line. Though the support material firmly engages theline, it does so with a protective or buoyant touch.

I have found that there are several materials and structures withVarious degrees of faineance. One highly faineant material is drycolloidal silica, specifically CAB-O-SIL type M-S sold by CabotCorporation, High St., Boston 10, Mass, USA. This is an extremely finepowdery material weighing about one-half pound per cubic foot. If asmall quantity of this material is pressed between two polishedsurfaces, such as glass plates, it will spread out into asemitransparent smudge about 0.001 inch thick. This surface, or smudge,of colloidal silica will then provide a faineant support for a delayline. Two such plates, when clamped to said line, smudge sides towardthe elastic line, show no observable eifects on the transmissioncharacteristics of the line even at a high pressure, say ten pounds to athreeinch length of line.

I have found that a piece of balsa wood, such as is used for modelairplanes, imposes no distortion on the signal of a delay line such asthat of FIG. 1, operating in the torsional mode, when clamped againstthe line with the fibers of its grain parallel to the wire of the line.

in the torsional mode, its vibration is circular about the axis of thewire. Thus the surface of the wire moves parallel to itself andtransverse the fibers of balsa that lie parallel to the wire. Similarly,fibrous glass filaments imposed no distortion on such a delay line whenused as a support therefor with the glass fibers lying parallel to thetorsional elastic line.

I have discovered that some other highly faineant ma terials aresandpaper, emery paper and the like. Specifically, I have employed twosheets of a 240-grit sandpaper, clamped with the grit sides toward thewire of a delay line of .025 inch NiSpan operating in the torsionalmode, and have observed substantially no change in the amplitude orshape of the output signal. I have found equally good results with suchsandpaper having paper and cloth backings, and with silicon carbide gritglued to a block of methyl methacrylate. However, sandpaper with largerand smaller grits, for example, 160-grit and 400-grit, were slightlyless faineant on such a line in that, when clamped to the wire, theyimposed barely perceptible phase distortions on the signals thereon.Other grits including alumina, silica, and garnet, and also diamond dustare also suitable.

In the construction of FIGS. 1 and 2, the wire 10 of the delay line issupported on twelve faineant pads 22. Alternate pads are fastened to thesupporting plate 8 and lie under the wire. The others are supported overthe wire by bars 24 which are adjustably supported by screws 26. Thescrews 26 are turned down to deflect the wires sufiiciently to developthe desired pressure between the wire 10 and the supports. Each end ofthe wire 10 overhangs one of the lower supports and, at each of thesepositions, a clamping bar 27 carries an additional small piece 29 of thefaineant material which, as best seen in FIG. 2, is clamped directlyagainst the wire for providing the position control required by theribbons 12.

The supporting pads 22 may have a flat surface, but preferably I providea series of grooves 23, as shown in FIG. 2, for receiving the turns ofthe wire 10. These grooves facilitate the assembly and provide assuranceagainst accidental displacement of the wires in the completed device.

The pads 22 may consist of blocks of bonded grit, such as siliconcarbide, alumina, silica, garnet or diamond, or a piece of balsa.

Alternative constructions for the faineant supports for use in thestructure of FIG. 1 are shown in FIG. 3 to FIG. 11. In FIGS. 3 and 4, asupport includes a block 32 of metal, glass, porcelain, methylmethacrylate or the like, having rectangular grooves lined with a grit34, such as silicon carbide, silica, alumina, garnet or diamond. Thegrit 34 may be applied to the base 32 by means of a glue or it may beapplied by pressing it into the softer material for thereby charging theblock 32 with the grit. Similar blocks with the grit-lined grooves areprovided for both the upper and lower pads as in the structure ofFIG. 1. As an alternative to clamping the ends of the wire 10 in thefaineant supports as in FIG. 1, a guide and positioner 36 of knownconstruction is provided.

In FIG. a block of metal, glass, porcleain, methyl methacrylate, orother plastic, 40 has applied thereto a surface 42 of colloidal silica,sandpaper, glass filaments, or balsa for supporting the coils of thewire 10. The colloidal silica is a self-adhering smudge. The sandpaper,glass filaments, or balsa, may be laid loose on the block 40 butpreferably is held by glue. Alternatively the block of the supportingpad may be supplied with shallow grooves for the wire as shown in FIG. 6or deeper grooves as shown in FIG. 7. The wiresupporting surfaces of theblocks 44 and 46 of FIGS. 6 and 7 may carry a surface of colloidalsilica, sandpaper, glass filaments, or balsa. In each of FIGS. 5,

6 and 7, the glass filaments and the balsa are arranged with thefilaments and the grain oriented parallel to the wire 10.

Instead of utilizing beam-like stresses in the wire 10 for developingthe support pressures, clamping supports as shown in FIGS. 8 and 9. maybe provided. As there shown, the coils of the wire 10 are clampedbetween two blocks 50 and 52, the clamping force being controlled by aspring 54 and adjusted by a screw 56. The surfaces of the blocks 50 and52 which engage the wire 10 carry colloidal silica, grit, sandpaper,glass filaments, or balsa. Alternatively, the blocks used in clamps ofFIG. 9 may be grooved as shown in FIG. 10 to improve the security of thestructure against lateral displacement of the wires 10. The groovesshould be shallow enough that the blocks 62 and 64 do not themselvestouch, so that the clamping forces are applied to the wires. Theclamping surfaces consist of a faineant material, such as colloidalsilica, grit, sandpaper, glass filaments, or balsa.

In FIG. 11, short, steel .blades with knife edges are molded into blocks72 and 74 of a rigid plastic material for supporting the wire 10 of thedelay line of FIG. 1. The knife edges engage and support the wire 10,extend parallel to the axis of the wire 10, and preferably are fromone-sixteenth to a quater of an inch long.

I believe the characteristic that makes these materials and structureshighly faineant is the presentation to the wire 10 of the delay line, ofmany contact elements of small area, which elements are highly compliantto the vibratory excursions of the wire surface, and small enough thatnegligible inertia is associated with the movement. I believe that theparticles of the colloidal silica act as rolling elements. I believethat the grit of the sandpaper, the grit glued to blocks, and the thinknife edges accommodate the rotary motion of the wire surface bydeflection. I believe that the glass filaments and the cellular strandsor fibers of the balsa, which present striate surfaces to the wire,accommodate the movement of the wire surface by a lateral rollingmovement of the striae, or strands. I believe that the superiorperformance of the 240-grit over that of the larger and smaller gritsresults from an optimum balance between opposing effects. I think thatin the finer grits the increase in number of contact points is greaterthan the increase in compliance of the smaller particles, and that inthe larger grits the increase of stiffness of the larger particles isgreater than the reduction of the number of contact points. I

In a structure such as that of FIG. 1, the support material extendsalong approximately five percent of the total length of the wire 10 and,within that small total length, actually touches the wire only atspaced, smallarea, contact points.

I think that a firm contact is required between the wire and the supportand that the supporting surfaces should be small enough to developcontact pressures that develop stresses at, or just below, half of theyield point. This condition places the static stress in the middle ofthe elastic range and permits maximum vibratory forces without reachingeither zero contact pressure or the yield point.

Preferably, in the normal operation of a delay line, neither the supportmaterial nor the surface of the wire should be stressed to its yieldpoint. However, the structure can be set by carrying the stresses abovethe yield point. For example, a delay line such as is shown in FIG. 1with grit-surfaced supports, when initially constructed and tested, willshow a low signal distortion. If the structure is then subjected to highaccelerations under vibration, for example, accelerations of fifty timesthe acceleration of gravity, the distortion is thereby increasedsomewhat, and the increased distortion of the signal persists when theline is thereafter operated without vibration. I believe that the setoccurs because the high acceleration forces cause the material to bestressed beyond the yield point with consequent small permanentdeformations, and that these deformations impair the sharpness and smallarea character of the contact between the line and support material. Thedeformation may occur in either the wire or its support. A delay line soset will be stable when subjected to acceleration forces up to the valueof the forces that caused the set.

Although the balsa may appear to have characteristics markedly differentfrom the grits. I believe it provides the faineant support for the delayline for the same reason, namely, that it provides numerous small-area,contacting portions with high compliance and low inertia.

It will be apparent that the invention may be employed in embodimentsother than those herein specifically shown and described and is to belimited only within the scope of the appended claims.

I claim:

1. In combination in a delay line, an elongate member, means forpropagating elastic waves along said member, and a support for saidmember comprising dry colloidal silica in engagement with said elongatemember.

2. The combination of claim 1 wherein said support comprises a rigidmember having a thin surface layer of dry colloidal silica in engagementwith said elongate member.

3. The combination of claim 1 wherein said support comprises two rigidmembers each having a thin surface layer of dry colloidal silica betweenwhich said elongate member is clamped.

4. In combination in a delay line, an elongate member, means forpropagating elastic waves along said member, and a faineant support forsaid member including a support member having a surface of grit inengagement with said elonagte member.

5. The combination of claim 4 wherein said support member includes asurface of hard grit in engagement with said elongate member.

6. The combination of claim 4 wherein the surface of said support membercomprises a gut of hard mate rial glued to said support member.

7. The combination of claim 4 wherein said support comprises a sheet 0fsandpaper with the grit side in contact with said elongate member.

8. The combination of claim 4 wherein said grit consists of siliconcarbide.

9. The combination of claim 4 wherein there are two support members withsurfaces of hard grit between which said elongate member is clamped.

10. An acoustic delay line comprising a round wire of a nickel-ironalloy, approximately .03 inch in diameter along which an elastic wave ispropagated, and a support for said wire having a surface of sandpaper ofapproximately 240-g-rit engaging said wire.

11. In combination in a delay line, an elongate member, means forpropagating an elastic wave along said member, a support member for saidelongate member, said support member having small surface protuberancesfor providing a supporting contact with said elongate member at smallareas, said supporting protuberances being compliant to the surfacevibration of said elongate member and having low inertia.

12. The combination of claim 11 wherein said protuberances are composedof a hard material.

13. The combination of claim 11 wherein said protuberances makesubstantially point contacts with said elongate member.

14. The combination of claim 11 wherein said protuberances makesubstantially line contact with said elongate member.

15. A faineant support for an acoustic delay line wherein an elasticsignal wave is propagated along an elongate member, said supportcomprising a member having surface protuberances of a hard materialmaking contact with said member substantially only at many small points.

16. A support for an acoustic delay line wherein an elastic signal waveis propagated along an elongate member, said support having a surface ofhard, granular,

material touching the elongate member at small sharp points.

17. In combination in a delay line, an elongate elastic member, meansfor propagating elastic waves along said member in the torsional mode,and a faineant support for said member comprising narrow, elongateelements oriented longitudinal to said elastic member and engaging italong narrow elongate areas.

18. The combination of claim 17 wherein said elongate elements of saidsupport comprise fiber-like strands.

19. The combination of claim 17 wherein said faineant support includes asurface of balsa with the fibers of the grain thereof engaging, andlying parallel to, said elongate plastic member.

20. In combination in a delay line, an elongate elastic member, meansfor propagating elastic waves along said member in a predeterminedvibratory mode of said member, and a faineant support for said membercomprising narrow, elongate elements engaging a surface of said member,which surface moves parallel to itself when said member carries anelastic wave in said predetermined mode, said elements being orientedtransverse the direction of vibratory motion of said surface when saidmember carries an elastic wave in said predetermined mode, said elementsengaging said member along narrow, elongate areas and presenting astriate surface to said elongate elastic member.

21. The combination of claim 20 wherein said support has a surface offiber-like material which includes said elongate elements and whichengages and supports said elastic member.

22. The combination of claim 20 wherein said support has a surface ofbalsa engaging and supporting said elastic member, the fibers of thebalsa constituting said elongate elements.

23. In combination in a delay line, an elongate elastic member, meansfor propagating elastic waves along said member in a predeterminedtorsional vibratory mode of said member, and a faineant support for saidmember comprising narrow, elongate elements engaging a surface of saidmember, which surface moves parallel to itself when said member carriesan elastic wave in said predetermined torsional mode, said narrow,elongate elements engaging said elastic member along narrow, elongateareas, said elements and areas being oriented transverse the directionof vibratory motion of said surface when said member carries an elasticwave in said predetermined torsional mode, said elements and areas beingnarrow compared to the dimensions of said member.

References Cited UNITED STATES PATENTS 2,629,770 2/1953 Sproule 333-302,727,214 12/1955 McSkimin 333-30 2,837,721 6/1958 Millership 333-302,842,687 7/1958 Van Dyke 3109.l 2,861,248 11/1958 Beistle et al. 333-303,011,136 1l/1961 Scarrott 333-30 3,113,223 12/1963 Smith et al. 310-9.lX 3,155,926 11/1964 Meitzler 333-30 3,241,090 3/1966 Bastian 333--30FOREIGN PATENTS 1,199,735 6/1959 France.

OTHER REFERENCES Scarrott, G. C., and Naylor, R., Wire-Type AcousticDelay Lines for Digital Storage, in Proceedings of the Institution ofElectrical Engineers, London, vol. 103, part B, Supplement No. 3, 1956,page 500 relied on.

HERMAN KARL SALLBACH, Primary Examiner. ELI LIEBERMAN, Examiner.

L. ALLAHUT, Assistant Examiner.

23. IN COMBINATION IN A DELAY LINE, AN ELONGATE ELASTIC MEMBER, MEANSFOR PROPAGATING ELASTIC WAVES ALONG SAID MEMBER IN A PREDETERMINEDTORSIONAL VIBRATORY MODE OF SAID MEMBER, AND A FAINEANT SUPPORT FOR SAIDMEMBER COMPRISING NARROW, ELONGATE ELEMENTS ENGAGING A SURFACE OF SAIDMEMBER, WHICH SURFACE MOVES PARALLEL TO ITSELF WHEN SAID MEMBER CARRIESON ELASTIC WAVE IN SAID PREDETERMINED TORSIONAL MODE, SAID NARROW,ELONGATE ELEMENTS ENGAGING SAID ELASTIC MEMBER ALONG NARROW, ELONGATEAREAS, SAID ELEMENTS AND AREAS BEING ORIENTED TRANSVERSE THE DIRECTIONOF VIBRATORY MOTION OF SAID SURFACE WHEN SAID MEMBER CARRIES AN ELASTICWAVE IN SAID PREDETERMINED TORSIONAL MODE, SAID ELEMENTS AND AREAS BEINGNARROW COMPARED TO THE DIMENSIONS OF SAID MEMBER.